The invention pertains to a sensing device for indicating changes in ink film thickness on the ink transfer rollers of a printing press and more particularly to a device utilizing a circuit having a pair of spaced light emitting diodes disposed in operative association with a measuring and reference surface formed by a division of the periphery of a guage wheel. The difference between the signals obtained from each of these surfaces through their respective light emitting diode is completed to provide a resultant signal proportional to the thickness of the ink film.
U.S. Pat. No. 3,707,123 discloses an apparatus for detecting changes in thickness of ink film on the roller system of a printing press which utilizes a pair of photocells. One of these photocells is disposed within a transparent roller that is in contact with a printing press roller and serves to generate a film thickness signal while the other serves to generate a reference signal.
Other U.S. patents show and describe devices that utilize light rays to measure the thickness of sheet materials, and for reference to the teachings of such disclosures, attention is hereby directed to U.S. Pat. Nos. 1,963,128 and 3,518,441.
The present invention provides an improved means for measuring the ink film thickness on the inking rollers of a printing press, for the reference and measuring surfaces are formed on the same base of a rotatable gauge wheel that is disposed in operative association with said inking roller thereby causing all variables to remain constant. In other words, with these surfaces having a common base portion, any difference due to expansion, contraction, out-of-roundness, etc., will have no affect on the thickness measurement of the ink film.